ATK Mohun Bagan took a 3-0 lead going into the break before adding two more goals to seal the victory.
The result means ATK Mohun Bagan will face Bangladesh club Abahani Dhaka in the South Playoff for a place in the Group Stage.
ATK Mohun Bagan are bidding to qualify to the AFC Cup group stage for the second consecutive time, while Blue Star SC came into the tie having defeated Nepal’s Machhindra FC 2-1 in the first preliminary round.
Blue Star came closest to finding the net in the 12th minute when Mohamed Fahir sent a dangerous long ball to Prince Boadu, whose close-range effort was foiled by ATK Mohun Bagan goalkeeper Arsh Anwer.
However, ATK Mohun Bagan’s patience was finally rewarded in the 24th minute when Manvir Singh and Kiyan Giri had their shots blocked but the rebound fell to Joni Kauko, who stabbed home from inside the box for the opener.
ATK Mohun Bagan doubled their lead in the 29th minute when Manvir Singh intercepted Blue Star’s T. Kajakopan before beating the offside trap to slot the ball through the legs of goalkeeper Lakpriya Fernando.
Blue Star suffered more woe 10 minutes later when they conceded a penalty following a handball, with Kauko making no mistake from the penalty spot to give ATK Mohun Bagan a 3-0 lead going into the break.
ATK Mohun Bagan dominated the second half but could not increase their tally early on with Manvir Singh, Hugo Boumous and David Williams all failing to score past Fernando.
Juan Ferrando’s side added their fourth goal of the evening after Boumous sent Manvir Singh free on the right flank before the forward sent an inch perfect pass to Williams to score from close range in the 77th minute.
Manvir Singh scored the fifth and final goal when he beat the Blue Star defenders before slotting home past Fernando to seal the emphatic win.